Lithium imide salts such as LiN(CF3SO2)2 in a nonaqueous solvent can cause corrosion to metal collectors, most typically aluminum foil, in lithium secondary batteries. Corrosion of the aluminum foil can shorten the battery life, rendering the battery impractical for some applications. However, if this corrosion can be reduced or limited, the life of the battery can be extended, increasing its usefulness. It is well known to one skilled in the art that lithium imide salts have superior thermal and hydrolytic stability compared to lithium hexafluorophosphate commonly used in Li-ion batteries.
Li et al. in U.S. Pat. No. 7,348,102 describes a metal current collector with a carbon coating to protect against corrosion in lithium secondary batteries. However, the electrolyte employed is of molten salt, not a lithium salt electrolyte in a mixture or in organic solvents.
Ro et al. in U.S. Pat. No. 7,327,556 discloses the use of aluminum metal coated with carbon. The carbon coating on the aluminum surface improves the adhesion of an applied active material. However, the coating is not used for corrosion prevention in rechargeable lithium cells, and the electrolyte described does not corrode aluminum.
So-Hyun Hur et al. in KR Pat. No 10-2006-0114543 describes the use of a lithium salt mixture of LiPF6 and a lithium-imide-based salt. However, no protective, conductive coating is employed. The mixture of salts, especially with lithium imide salts, can cause corrosion in lithium-ion cells, resulting in cell degradation and loss of performance.
In view of the shortcomings of the prior art, the present invention provides lithium or lithium-ion electrochemical cells, wherein corrosion is reduced and the life of the battery is extended, thereby increasing its usefulness.